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TrustPilotChallenge/dotnet/WhiteRabbit/PhraseSet.cs

67 lines
2.5 KiB

using System.Numerics;
namespace WhiteRabbit
{
// Anagram representation optimized for MD5
internal unsafe struct PhraseSet
{
private const int WordIndexMask = unchecked((int)(((uint)-1) << 16));
private const int WordIndexIncrement = ((int)1) << 16;
private const int CharIndexMask = ((int)1 << 16) - 1;
public fixed uint Buffer[8 * Constants.PhrasesPerSet];
public PhraseSet(byte[][] words, int[][] permutations, int offset, int numberOfCharacters)
{
fixed (uint* bufferPointer = this.Buffer)
{
var length = numberOfCharacters + words.Length - 1;
for (var i = 0; i < Constants.PhrasesPerSet; i++)
{
var permutation = permutations[offset + i];
var startPointer = bufferPointer + i * 8;
var currentPointer = (byte*)startPointer;
byte* lastPointer = currentPointer + length;
int currentState = 0; // wordIndex << 16 + charIndex
byte[] currentWord = words[permutation[0]];
for (; currentPointer < lastPointer; currentPointer++)
{
currentWord = words[permutation[currentState >> 16]];
*currentPointer = currentWord[(currentState & CharIndexMask)];
currentState++;
var nextStateNextWord = new Vector<int>((currentState + WordIndexIncrement) & WordIndexMask);
currentState = Vector.ConditionalSelect(Vector.GreaterThanOrEqual(new Vector<int>(currentState & CharIndexMask), new Vector<int>(currentWord.Length)), nextStateNextWord, new Vector<int>(currentState))[0];
}
*currentPointer = 128;
startPointer[7] = (uint)(length << 3);
}
}
}
public byte[] GetBytes(int number)
{
System.Diagnostics.Debug.Assert(number < Constants.PhrasesPerSet);
fixed(uint* bufferPointer = this.Buffer)
{
var phrasePointer = bufferPointer + 8 * number;
var length = phrasePointer[7] >> 3;
var result = new byte[length];
for (var i = 0; i < length; i++)
{
result[i] = ((byte*)phrasePointer)[i];
}
return result;
}
}
}
}